Improve sublayout for DualLayout

[dlfivefifty]

No description provided.

[codecov]

Codecov Report

Merging #39 into master will increase coverage by 1.09%.
The diff coverage is 85.00%.

@@            Coverage Diff             @@
##           master      #39      +/-   ##
==========================================
+ Coverage   80.75%   81.84%   +1.09%     
==========================================
  Files           9        9              
  Lines        1226     1289      +63     
==========================================
+ Hits          990     1055      +65     
+ Misses        236      234       -2     

Impacted Files	Coverage Δ
src/memorylayout.jl	80.47% <80.00%> (+1.29%)	⬆️
src/ArrayLayouts.jl	71.87% <86.66%> (+2.90%)	⬆️
src/triangular.jl	95.67% <0.00%> (+0.33%)	⬆️
src/factorizations.jl	92.30% <0.00%> (+0.42%)	⬆️
src/lmul.jl	84.31% <0.00%> (+0.64%)	⬆️
src/ldiv.jl	76.92% <0.00%> (+0.68%)	⬆️
src/mul.jl	70.07% <0.00%> (+0.90%)	⬆️
src/diagonal.jl	68.00% <0.00%> (+1.33%)	⬆️
... and 1 more

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